Prince Philip was not made king due to longstanding British royal tradition: when a man marries a Queen, he does not automatically take the male version of the title. Elizabeth II designated him a Prince and later Duke of Edinburgh; he never held the title of king. In short, the position was a matter of protocol and title rules, not personal choice. This is why his wife could be Queen, but he remained Duke (and later Prince) rather than King .[3][5]
Sources
The Duke of Edinburgh died on Friday at 99.
www.marieclaire.comThere's a reason that 'King consort' doesn't exist
www.goodto.comPhilip was once the prince of Denmark and Greece, before marrying Queen Elizabeth nearly 74 years ago.
www.cbsnews.comThough he was married to a queen, he was named a prince for a reason
www.harpersbazaar.comWhy wasn’t Prince Philip a king? Prince Philip did not have the title of king because of British royal tradition whereby a man marrying into the royal
www.britannica.comPRINCE PHILIP has been described as the Queen's "strength and stay". But despite being her most loyal companion, why is the Duke of Edinburgh not a King, or a King Consort?
www.express.co.ukQueen Elizabeth II and Prince Philip were together for 73 years but why was the Duke of Edinburgh never king but Camilla is Queen Consort?
royal-insider.comWhen Philip Mountbatten married into the royal family way back in 1947, he became the Duke of Edinburgh along with a number of other titles.
www.standard.co.uk